This invention relates to a system for representing line drawings by polygonal lines in which a line drawing is read as binary digital data, and the binary digital data are converted into polygonal line data.
A method of representing a line drawing by polygonal lines is often employed for data compression or data reuse, as is well known in the art. More specifically, the following three methods have been employed for representing line drawings by polygonal lines:
(1) A first method in which a line drawing is represented by a number of thin lines, and the resultant picture elements are traced (cf. Japanese Patent Application Unexamined Publication Nos. Hei. 1-134682 and Hei. 1-142880).
(2) A second method in which the contour lines of an image are extracted, and the center lines of the contour lines thus extracted are obtained.
(3) A third method in which an image is divided into a number of squares arranged in a matrix form, and the local pattern of each square is identified (cf. Japanese Patent Application Unexamined Publication No. Sho. 62-191988).
However, these methods are disadvantageous in that, since it is necessary for each of the methods to employ an image processing technique which accesses an image in its entirety, the image processing time is necessarily long, and it is essential to provide a large capacity memory because the image must be kept in memory during the image processing time.
On the other hand, a method has been employed in which polygonal lines are obtained from run data (cf. Japanese Patent Application Unexamined Publication No. Sho. 63-45687). In the method, straight segments different in inclination are detected from the variation between the gravity center values of the m-th run and the (m-n)-th run. However, the method depends only on the local data called "run" in the image, and therefore it cannot determine whether or not the run can be represented by polygonal lines. For instance, in the case of a solid arrow mark in a drawing, the method cannot detect its configuration from the run data.